Field of the Invention
The present invention relates to focus bracketing based on simultaneous image capturing from a plurality of viewpoints.
Description of the Related Art
Bracketing is one of image capturing methods for cameras. Specifically, bracketing is an image capturing method for continuously capturing a plurality of images within a short period of time while changing the image capturing settings. The photographic image quality, which is difficult to achieve with one image, can be realized by using a plurality of images obtained by bracketing.
Types of bracketing include, for example, exposure bracketing and flash bracketing. In exposure bracketing, continuous image capturing is performed while changing the exposure. In flash bracketing, continuous image capturing is performed while switching on and off the flash. One typical type of such types of bracketing is focus bracketing in which continuous image capturing is performed while changing the in-focus position (Japanese Patent No. 4997043).
Specifically, focus bracketing is an image capturing method for obtaining a plurality of images focused at different distances by capturing an image multiple times while changing the focus distance so that a proximal subject, an intermediate subject, and a distal subject sequentially come into focus, for example. During focus bracketing, the f-number of the lens is usually set to be small at the time of image capturing. This setting makes each image have a shallow depth of field but makes the amount of incident light for forming the image large, yielding a sharp image having relatively less image capturing noise than a deep-depth-of-field image captured with a large f-number.
A depth-of-field extending process such as the one disclosed in David E. Jacobs, Jongmin Baek, and Marc Levoy, “Focal Stack Compositing for Depth of Field Control”, Stanford Computer Graphics Laboratory Technical Report 1 (2012): 2012 is known as a usage of a plurality of images obtained by focus bracketing. Specifically, the depth-of-field extending process is a process for generating a deep-depth-of-field image having a wide in-focus range by combining a plurality of shallow-depth-of-field images focused at different distances. The use of this process can provide a deep-depth-of-field image having less noise than an image captured with a large f-number.
A common issue in bracketing is blurring of the subject in images due to a hand-induced camera shake or movement of the subject during image capturing. This issue arises due to continuous capturing of a plurality of images. Accordingly, it is effective to decrease a period of time taken for image capturing. For example, the issue can be dealt with by simultaneously capturing images using a camera including a plurality of image capturing units.
However, images obtained by simultaneous image capturing using the camera described above are images captured from different viewpoints. Accordingly, position alignment needs to be performed on the images before the images are combined in a process such as the depth-of-field extending process. A process for aligning positions of a plurality of images typically employs a method for deriving correspondences between images and shifting the individual images in accordance with the derived correspondences. However, because images obtained by focus bracketing are images having different in-focus states, it is difficult to derive correspondences between the images and thus to accurately determine image shifting amounts used in position alignment of the images.